222 
On the Theoretical and Practical Value of 
preceding articles of food from their respective market price, 
the feeding-value of linseed-cake vv^ould be 12Z. 10*. minus 
4Z. 125. 6c?., or 11. I85. 6f/. per ton ; that of decorticated cotton- 
cake 10/. minus 6/. IO5., or 3/. 10s. a ton; whilst the feeding-value 
of undecorticated cotton-cake will be 8Z. minus 3Z. I85. 6c?., or 
4/. 2s. 6c?. a ton ; that of rape-cake, 8Z. 15s. minus 4/. 18s. 6c?., or 
3/. 16s. 6f/. a ton, and that of barlej-meal, 9Z. 5s. minus 1/. 10s., 
or II. 15s. Whatever value may attach to the preceding estimates 
of the feeding- and manure-value of different cakes and of barley- 
meal, they afford convincing evidence of the importance of 
taking into account the manure-value of purchased foods in 
estimating their comparative total money-value. 
In my intercourse with agriculturists I have frequently met with 
intelligent and otherwise well-informed persons who have openly 
confessed that they had not much faith in Mr. Lawes's estimates 
of the manurial value of purchased food. In their minds evidently 
lurked the idea that these estimates are in a great measure 
fanciful, and rest on no solid foundation. It cannot therefore 
be stated in too plain language that the recognised superior 
fertilising properties of the manure of fattening stock fed upon 
cake is mainly due to the high percentage of its nitrogenous 
constituents, and that by far the greater portion of the nitrogen 
of the food is recovered in the manure. Associated with nitro- 
genous substances we always find phosphates and potash ; and 
food rich in nitrogenous substances will generally also produce 
manure richer in phosphates and potash, than food which is 
comparatively poor in nitrogenous constituents. 
The fact that decorticated cotton-cake is very rich in nitrogen, 
and also contains a good deal of phosphate of lime, is undisputed; 
nor is anybody likely to deny that the superior fertilising pro- 
perties of this description of cake depend mainly upon its 
richness in nitrogen. It is chiefly for the purpose of supply- 
ing available nitrogenous food that rape-cake is employed as 
a manure for cereal crops. 
On the light lands of Norfolk, in many parts of Kent, in 
some localities in Cambridgeshire, and in some other counties of 
England, rape-cake is a favourite manure with many farmers ; 
and they willingly pay 6/. per ton for manure rape-cake, which 
on an average contains not more than about 4J per cent, of 
nitrogen, or somewhat less than good green German feeding 
rape-cake. It is well known that rape-cake, and other residual 
cakes from the presses of oil-crushers, decompose with facility 
in light and porous soils, furnisliing thereby readily available 
food to plants, whilst on retentive clay-soils the decomposition 
of such cakes is too slow to meet the requirements of those crops 
